This feature (and some others) is available to try for an hour at a time, as often as you like. To keep it available permanently, you can become a supporter.

You don't have to pay more than once if you don't want to. You can become a supporter at whatever level you feel comfortable with, and not pay again unless you want to show your appreciation (kinda like a tip jar). After your supporter status expires, all of the advanced features that you had when you were a supporter will remain available permanently. Of course, I hope that people choose to support at the 12-month level, and choose to renew their support in the future, but there's no need if you don't think it's worth it.